1. Technical Field of the Invention
The invention relates generally to an optical system for scanning a laser beam. The invention is especially useful in connection with LADAR guidance systems. In particular, the invention relates to an optical system using two pairs of rotating prisms to direct a beam of collimated light, such as laser light into a desired scan area and, simultaneously, to sweep the beam in a predetermined scanning pattern.
2. Background of the Invention
Laser detection and ranging (xe2x80x9cLADARxe2x80x9d) guidance systems are known in the art. For example, missiles are conventionally provided with a LADAR guidance system used to correct the missile while in route onto a target. In these systems, a laser beam is directed from the missile in a scanning pattern over an area of interest, called the scanning area. The laser light reflected from the scanning area is detected by the missile, which then uses the reflected laser light to generate an image of the scanning area. Computer systems on board the missile identify the target from the image and operate the missile""s control surfaces, directing the missile to the target.
Useful guidance systems must have a mechanism for scanning the laser beam in a desired pattern over the scanning area. Conventional mechanisms for LADAR guidance systems typically use fixed speed prisms, gimbals, articulated mirrors, and other optical components to direct and scan the beam. These components are undesirable because they tend to be bulky, delicate, and expensive. Further, current LADAR scanners are either limited to low scan rates, or achieve high scan rates by being limited to a single, fixed scan pattern. The present invention overcomes these disadvantages, and provides further improvements and advantages as will become clear to those skilled in the art in view of the following disclosure.
One aspect of the invention relates to an LADAR guidance system that can be used to guide a moving vehicle, such as a missile, to a target. In this version of the invention, the optical system includes two pair of optical prisms, a forward pair and a rear pair. The prisms in the forward pair may be positioned with respect to each other to direct the outgoing laser beam, and hence, the scan pattern produced by the rear prisms, in a particular direction relative to the vehicle. The rear pair of prisms may be positioned with respect to each other to move the outgoing laser beam in such a manner that the beam is scanned in a desired pattern. In other words, the rear pair produces the pattern, and the front pair directs or steers the centroid of the pattern to a desired location in the scan area.
In a more specific version of the invention, the optical prisms are arranged in concentric tubes that are mechanically connected to precision motors that rotate the tubes, and hence the prisms, with respect to each other. The precision motors are operated by the vehicle""s onboard computer system, which, by rotating the prisms, can scan the beam in any particular pattern onto a desired scan area. This not only allows the use of multiple scan patterns, of any desired size, but also allows the scan patterns to be moved to track moving targets.
In another advantageous version of the invention, the motors controlling the prisms may be connected to other vehicle computer systems to improve performance. For example, it is advantageous to connect the front prisms to the inertial measurement unit, which detects variations in the vehicle""s flight path. This allows information from the inertial measurement unit to operate the front prisms so as to cancel out the effects of vehicle vibration and flight variations on the direction of the outgoing laser beam.